Method for producing highly reactive polyisobutenes

ABSTRACT

A process for the preparation of highly reactive polyisobutenes is described, in which isobutene is polymerized in the presence of a complex of boron trifluoride and at least one cocatalyst in a liquid organic phase at a reaction temperature of from −60 to −4° C. and water is added in two stages to the organic phase for catalyst deactivation and catalyst extraction.

[0001] The present invention relates to a process for the preparation ofhighly reactive polyisobutenes.

[0002] The highly reactive polyisobutenes discussed are those which havea high content of, preferably, more than 60 mol % of terminal vinylidenegroups. Highly reactive polisobutenes are desirable intermediates forthe production of additives for lubricants and fuels.

[0003] Such highly reactive polyisobutenes are obtainable, for example,by the process of EP 0 628 575, by cationic polymerization of isobutenein the liquid phase with the aid of boron trifluoride and a secondaryalcohol at from 0 to −60° C.

[0004] The prior Patent Applications DE 199 48 947.5, DE 199 52 031.3,DE 199 52 030.5, DE 100 28 585.6 and DE 100 35 298.7 relate toimprovements or advantageous embodiments of such a process.

[0005] After reaching the desired molecular weight, the polymerizationcatalyst is deactivated and the polymerization is stopped in thismanner. EP 0 628 575 recommends for this purpose passing the reactiondischarge into a medium, such as water, an alcohol, acetonitrile,ammonia or an aqueous solution of a mineral base, such as an alkalimetal or alkaline earth metal hydroxide solution or a solution of acarbonate of one of these metals.

[0006] For the preparation of highly reactive polyisobutenes, it iscritical that the polymerization catalyst is deactivated as rapidly andquantitatively as possible after the desired molecular weight has beenreached, in order to prevent isomerization reactions givingpolyisobutene molecules in which the double bond assumes athermodynamically more favorable position in the interior of themolecule.

[0007] Organic chain-terminating agents, such as acetonitrile andalcohols, have the advantage that they are miscible with the organicreaction phase and can therefore be readily and uniformly distributed insaid phase. However, they have the disadvantage that their affinity tothe BF₃ molecule is comparatively low and they therefore lead only togradual catalyst deactivation. Since they can also act as phasemediators, they complicate the subsequent extraction with water forremoval of the catalyst deactivation products.

[0008] Aqueous chain-terminating agents, in particular water itself,have the advantage that the catalyst deactivation and removal of thecatalyst deactivation or hydrolysis products by extraction can takeplace simultaneously. The disadvantage however is that the aqueous phaseis immiscible with the organic reaction phase and the catalystdeactivation can take place only at the phase boundary. In continuousregions of the organic reaction phase, the polymerization reaction canstill continue or undesired isomerizations can take place after theorganic reaction phase has been brought into contact with an aqueouschain-terminating agent.

[0009] JP-A 7196724 discloses a process for removing a Lewis acidcatalyst, used for carrying out a cationic polymerization, from theorganic reaction phase, in which the reaction phase is treated withwater or acidified water and separation into a polymer-containingorganic phase and an aqueous phase containing the dissolved catalyst iseffected. The water or acidified water is preferably preheated in orderto promote the removal of the catalyst. The amount of water or acidifiedwater is at least 5, preferably at least 20, in particular at least 40,% by volume, based on the reaction phase. The preparation of highlyreactive polyisobutenes is not discussed.

[0010] U.S. Pat. No. 4,940,833 describes a process for working up aliquid polymerization reaction mixture which contains olefin monomer,catalyst residues and catalyst deactivation products, in which themixture is washed with water and the organic and aqueous phase are thenseparated. Oxygen-containing compounds, such as alcohols, dicarbonylcompounds and/or alkylene oxides, are mentioned as preferred catalystdeactivators, methanol being most preferred.

[0011] It is an object of the present invention to provide a process forthe preparation of highly reactive polyisobutenes which permits rapidand substantially quantitative catalyst deactivation and simpleextraction of the catalyst deactivation products.

[0012] We have found that this object is achieved, according to theinvention, by a process for the preparation of highly reactivepolyisobutenes, in which

[0013] a) isobutene is polymerized in the presence of a complex of borontrifluoride and at least one cocatalyst in a liquid organic phase at areaction temperature of from −60 to −4° C.,

[0014] b) the organic phase which is substantially at the reactiontemperature is brought into intimate contact with a first portion ofwater whose temperature is at least 80° C., preferably at least 90° C.,above the reaction temperature, with formation of an emulsion whichcontains finely dispersed water droplets in the organic phase,

[0015] c) a second portion of water is added to the emulsion withformation of a continuous, predominantly organic phase and a continuous,predominantly aqueous phase, and

[0016] d) the organic phase is separated from the aqueous phase.

[0017] The present invention is based on the finding that, for thesubstantially quantitative extraction of the boron trifluoridecocatalyst complex or of the hydrolysis products thereof from theorganic reaction phase, the amount of aqueous phase may not fall below aminimum amount, based on the organic reaction phase. If, however, theorganic reaction phase and an amount of aqueous phase which correspondsto the required minimum amount or is greater than this are brought intocontact, it is found that the phases have a considerable tendency tophase separation with the formation of a continuous organic phase and acontinuous aqueous phase. This situation makes it more difficult todisperse the aqueous phase finely in the organic reaction phase, whichdispersing is necessary for achieving rapid, quantitative and uniformcatalyst deactivation. In an attempt to carry out the catalystdeactivation using a smaller amount of water, it was found that contactof the aqueous phase with the reaction phase, which has a temperaturebelow the freezing point of water, can result in the formation of icecrystals which lead to blockage of pipelines and/or valves and do notpermit satisfactory catalyst deactivation.

[0018] The novel process avoids all of the problems described above. Inparticular, it is surprising that no undesirable isomerization reactionsoccur when the reaction phase is brought into contact with the firstportion of water whose temperature is at least 80° C. above the reactiontemperature.

[0019] Preferably, the sum of the first and second portions of water isfrom 5 to 100, in particular from 20 to 90, % by weight, based on theweight of the organic phase. The weight ratio of the first portion tothe second portion is preferably from 1:10 to 10:1, in particular from1:5 to 5:1, particularly preferably from 1:5 to 1:1.5.

[0020] Preferably, the emulsion obtained by bringing the organic phaseinto contact with the first portion of water has a mixing temperature offrom +5 to +50° C., in particular from +10 to +45° C.

[0021] The first and/or second portions of water can contain dissolvedsubstances, such as mineral bases, e.g. alkali metal or alkaline earthmetal hydroxides or carbonates, ammonia or acids, such as hydrochloricacid, etc. Since, however, no further advantage is generally associatedtherewith, the first and second portions of water preferably contain nosignificant amounts of dissolved substances. Tap water or river water issuitable. In general, however, demineralized water is preferred. The pHof the first and second portions of water is in general from 6 to 10.

[0022] The novel process is suitable for the preparation ofpolyisobutenes having a number average molecular weight of from 500 to 5000 and is particularly suitable for the preparation of polyisobuteneshaving a number average molecular weight of from 1 800 to 5 000. Thepolymerization in step a) of the novel process is therefore preferablycarried out in such a way that polyisobutene molecules having a numberaverage molecular weight of from 1 800 to 5 000 are obtained.

[0023] At the time of being brought into contact with the first portionof water, the organic phase is substantially at the reactiontemperature, i.e. it is not significantly heated after reaching thedesired degree of polymerization before the catalyst is deactivated byadding the first portion of water.

[0024] The first portion of water is preferably added by means of anozzle into a pipeline through which the organic reaction phase ispassed. The outlet orifice of the nozzle is preferably arranged in thedirection of flow of the organic phase. The formation of the emulsion isassisted if the stream of the organic phase in the region of theaddition of the first portion of water has turbulent flow. Measures forgenerating turbulent flows are known to a person skilled in the art. Thefirst portion of water typically has a temperature of from 80 to 160° C.Temperatures of more than 100° C. necessitate keeping the water under apressure which is higher than ambient pressure.

[0025] The addition of the second portion of water can likewiseadvantageously be effected via a nozzle into the stream of the emulsionobtained by bringing the organic phase into contact with the firstportion of water. The nozzle for adding the second portion of water isthen arranged a distance downstream of the nozzle via which the firstportion of water is added. A suitable spacing between the nozzles canreadily be determined by a person skilled in the art by means of simpleexperiments. The optimum spacing is as a rule dependent on the flow rateof the organic phase. As a rule, it is such that a time span of from 2to 1 000, in particular from 2 to 200, seconds elapses from the bringingof a volume element of the organic phase into contact with the firstportion of water to the addition of the second portion of water. Thesecond portion of water typically has a temperature of from 40 to 80° C.

[0026] After the addition of the second portion of water, the mixture oforganic phase and aqueous phase can be passed into a calming zone forseparation of the two phases and separated. This is expediently done ina horizontal, continuously operated phase separation vessel throughwhich flow takes place with a low flow rate. Owing to the differencebetween the densities of the phases, the mixture of the organic phaseand aqueous phase separates under the action of gravity so that the twophases are present in continuous form and substantially free of foreignphases, as layers one on top of the other.

[0027] Whereas in general no problems at all are encountered whenseparating off the main amount of the aqueous phase, the organic phaseoften also contains dispersed water droplets which do not coalescespontaneously. Complete phase separation on the basis of the densitydifference requires a very long residence time, with the result thateconomical removal of the final amounts of aqueous phase is notpossible. In order to remove the dispersed droplets of the aqueous phasewhich are still present after the main amount of the aqueous phases hasbeen separated off, the organic phase containing still dispersed waterdroplets is advantageously passed through an apparatus havingcoalescence-promoting internals, and the coalesced aqueous phase isseparated from the organic phase. The coalescence-promoting internalsare as a rule packings, coalescence surfaces or fine-pored internals.

[0028] The internals having coalescence surfaces are generally platepackets having corrugated or inclined surfaces on which disperseddroplets accummulate and initially form a film. If this film enclosesthe individual plate and is sufficiently thick, large drops of thedispersed phase form at the plate edge and fall down. They then form alayer which can be readily separated off mechanically. In the case offine-pored internals, the inner structure of the internals forces thefinely dispersed drops to come into contact with the internal surface,which drops then form a film and leave the hollow structure of thefine-pored internals in the form of combined larger drops.

[0029] Suitable packings are the packings usually used in distillation.Preferably, the organic phase containing dispersed droplets of theaqueous phase is passed through a bed of packings. Wetting of the largesurface of the packing results in surface coalescence andsimultaneously, as a result of drop movement, in drop-drop coalescence.

[0030] Coalescing filters in the form of filter cartridges whichconsist, for example, of polypropylene have proven particularly useful.

[0031] It has proven advantageous to mix the organic phase freed fromthe main amount of the aqueous phase with a third portion of waterbefore the passage through the apparatus having coalescence-promotinginternals. The third portion of water is, for example, from 0.5 to 10,in particular from 2 to 7, % by weight, based on the organic phase. Thetemperature of the third portion is not critical and is usually from 20to 60° C.

[0032] The polymerization of isobutene can be carried out continuouslyor batchwise but is preferably effected continuously. Processes forcontinuous polymerization in the presence of a complex of borontrifluoride and at least one cocatalyst in a liquid organic phase areknown per se. In a continuous process, a part of the reaction mixtureformed in the polymerization reactor is discharged continuously. Anamount of starting materials, in this case isobutene orisobutene-containing feed, which correspond to the discharge is fedcontinuously to the polymerization reactor. The ratio of the amount ofsubstances present in the polymerization reactor to the amount which isdischarged is determined by the circulation/feed ratio which, in thecase of the continuous polymerization of isobutene to polyisobutene, isas a rule from 1 000:1 to 1:1, preferably from 500:1 to 5:1, inparticular from 50:1 to 200:1. The average residence time of theisobutene to be polymerized in the polymerization reactor may be fromfive seconds to several hours. Residence times of from 1 to 30, inparticular from 2 to 20, minutes are particularly preferred.

[0033] The polymerization of the isobutene is carried out in theconventional reactors, such as stirred kettles, tubular reactors,tube-bundle reactors and loop reactors, loop reactors, i.e. tubularreactors or tube-bundle reactors having the characteristics of a stirredkettle, being preferred. Tubular reactors having tube cross-sectionswhich lead to turbulence in segments are particularly advantageous.

[0034] The polymerization is carried out at a reaction temperature offrom −60 to −4° C., in particular from −25 to −5° C. The heat ofpolymerization is removed appropriately with the aid of a coolingapparatus. This may be operated, for example, with liquid ammonia as acoolant. Another possibility for removing the heat of polymerization isevaporative cooling. Here, the heat liberated is removed by partialevaporation of the reaction mixture, for example of the isobutene and/orother readily volatile components of the isobutene feed or of a readilyvolatile diluent. Isothermal conditions are preferably employed, i.e.the temperature of the liquid organic reaction phase in thepolymerization reactor has a constant value and changes only slightly,if at all, during the operation of the reactor.

[0035] The concentration of the isobutene in the liqiud reaction phaseis as a rule from 0.2 to 50, preferably from 0.5 to 20, % by weight,based on the liquid organic phase.

[0036] Suitable starting materials are both isobutene itself andisobutene-containing C₄-hydrocarbon streams, for example refined C₄fractions, C₄ cuts from the dehydrogenation of isobutane and C₄ cutsfrom steam crackers or FCC crackers (fluid catalysed cracking), providedthat they have been substantially freed from 1,3-butadiene containedtherein. Suitable C₄-hydrocarbon streams contain, as a rule, less than500 ppm, preferably less than 200 ppm, of butadiene. The presence of1-butene and cis- and trans-2-butene is substantially uncritical. Theisobutene concentration in the C₄-hydrocarbon streams is typically from40 to 60% by weight. When C₄ cuts are used as starting material, thehydrocarbons other than isobutene play the role of an inert diluent, asexplained below. The isobutene-containing feed may contain small amountsof contaminants, such as water, carboxylic acids or mineral acids,without there being any critical decreases in yield or selectivity. Itis expedient to avoid an enrichment of these impurities by removing suchpollutants from the isobutene-containing feed, for example by adsorptiononto solid adsorbents, such as active carbon, molecular sieves or ionexchangers.

[0037] Owing to the high viscosity of polyisobutene, it is advantageousto carry out the polymerization in the presence of an inert diluent. Theinert diluent used should be suitable for reducing the increase in theviscosity of the reaction solution, which is to be observed during thepolymerization reaction, to such an extent that removal of the resultingheat of reaction can be ensured. Suitable diluents are those solvents orsolvent mixtures which are inert to the reagents used. Suitable diluentsare, for example, saturated hydrocarbons, such as butane, pentane,hexane, heptane or octane, e.g. n-hexane, isooctane or cyclopentane,halogenated hydrocarbons, such as methyl chloride, dichloromethane ortrichloromethane, and mixtures of the abovementioned diluents, amongwhich n-hexane is particularly preferred. Before they are used, thediluents are preferably freed from impurities, such as water, carboxylicacids or mineral acids, for example by adsorption onto solid adsorbents,such as active carbon, molecular sieves or ion exchangers.

[0038] Boron trifluoride is expediently used in the form of gaseousboron trifluoride, it being possible to use technical-grade borontrifluoride still containing small amounts of sulfur dioxide and SiF₄,but highly pure boron trifluoride having a purity of about 99.5% byweight is preferably used.

[0039] Suitable cocatalysts are as a rule oxygen-containing compoundswhich preferably contain at least one divalent oxygen atom. Suitableoxygen-containing compounds in addition to water are organic compoundsof up to 30 carbon atoms. Examples of these are C₁-C₃₀-alkanols,C₁-C₃₀-cycloalkanols, C₂-C₁₀-diols, C₁-C₂₀-carboxylic acids,C₄-C₁₂-carboxylic anhydrides and C₂-C₂₀-dialkyl ethers. Preferred amongthese are monohydric alkanols of 1 to 20, in particular 1 to 4, carbonatoms, which, if required, can be used together with the C₁-C₂₀-dialkylethers. Particularly preferred cocatalysts are monohydric secondaryC₃-C₂₀-alkanols. Examples are isopropanol, 2-butanol, sec-pentanol,sec-hexanol, sec-heptanol, sec-octanol and the like. 2-Butanol and inparticular isopropanol are particularly preferably used.

[0040] The molar ratio of boron trifluoride to cocatalyst is preferablyfrom 1:1 to 1:10, in particular from 1:1.1 to 1:5, particularlypreferably from 1:1.2 to 1:2.5.

[0041] The concentration of the complex of boron trifluoride andcocatalyst in the reactor is as a rule from 0.01 to 1, in particularfrom 0.02 to 0.7, particularly preferably from 0.03 to 0.5, % by weight,based on the liquid organic phase.

[0042] After the desired degree of polymerization has been reached, afirst portion of water is added, as described, to the organic phasewhich is substantially at the reaction temperature, and a second portionof water is then added to the emulsion obtained.

[0043] The isobutene polymer contains, as a rule, more than 60, inparticular more than 80, mol % of terminal vinylidene groups. Thedispersity M_(w)/M_(n) is preferably not more than 1.8, in particularnot more than 1.6.

[0044] The working-up of the organic phase freed from the aqueous phase,for isolation of the desired polyisobutene, is carried out in aconventional manner. The polyisobutene is freed, as a rule bydistillation, from unconverted isobutene, inert diluent and anyisobutene oligomers and is obtained as a distillation residue, forexample as a bottom product of a distillation column.

[0045] The examples and comparative examples which follow illustrate theinvention.

EXAMPLES

[0046] For the preparation of a polyisobutene, the procedure accordingto EP-A 628 575, example 1, was followed: The isobutene-containing feedused corresponded to the following composition: Isobutane <1% by weightn-Butane <1% by weight 1-Butene <1% by weight trans-2-butene <1% byweight cis-2-butene <1% by weight Isobutene about 45% by weight Hexaneabout 54% by weight Butadiene <50 ppm Water about 2 ppm

[0047] In the course of one hour, 6 000 g of the above feed was fed tothe suction side of a loop reactor which was equipped with an integratedcirculation pump whose tube diameter was 30 mm and whose volume was 1000 ml. 1.6 times the molar amount, based on the boron trichloride (7.1mmol/l), of isopropanol was added. The reactor was cooled so that thetemperature in the reaction medium was −17° C. The average residencetime of the reaction medium in the reactor was 6.6 minutes.

[0048] Thereafter, the reaction discharge was first mixed, with the aidof a nozzle, continuously and thoroughly with X g per hour of water at90° C. and thus brought to a temperature of A° C. An average temperatureof the reaction discharge/water mixture of B° C. was then reached in thereaction discharge/water mixture after about 12 hours by continuousaddition of a further amount of Y g per hour of water at 60° C.

[0049] In a continuous 500 ml phase separation vessel, the aqueous phasewas then separated from the organic phase and a third portion of wateramounting to Z g per hour and having a temperature of 40° C. was addedcontinuously to the latter, once again by means of a nozzle.

[0050] The mixture thus obtained was passed continuously through a 100ml cartridge filter and a further 500 ml phase separation vessel, inwhich aqueous and organic phases were once again separated.

[0051] After the cartridge filter and the final phase separationdescribed, the organic phase was completely clear.

[0052] Analyses of the reaction discharge treated in this manner werecarried out for assessing the separation of fluorine from the reactiondischarge.

[0053] Furthermore, those analytical data of the polyisobutene obtainedafter removal of the volatile components by distillation which arerelevant for assessing the product quality were determined and arelisted below in the form of a table. TABLE A B X Y Z F Vin. ° C. ° C.g/h g/h g/h ppm Mn D % Ex. 1 4 32  700 1700 0  38 2236 1.766 86.2 2 4 35 700 1900 0  37 2229 1.763 86.5 3 6 38  800 1900 0  34 2270 1.756 85.9 44 32  700 1700 50  26 2287 1.759 86.3 5 4 32  700 1700 100  21 22811.773 86.9 6 4 32  700 1700 150  17 2278 1.698 87.1 Comp. Ex. 7 4 4 2600  0 0 121⁶⁾ 2132 1.811 69.2 ¹⁾ 8 −17 32   0 2600 0  42 2118 1.809 82.3²⁾ 9 ⁵⁾ 32  700 1900 0 — — — — ³⁾ ⁴⁾

We claim:
 1. A process for the preparation of highly reactivepolyisobutenes, in which a) isobutene is polymerized in the presence ofa complex of boron trifluoride and at least one cocatalyst in a liquidorganic phase at a reaction temperature of from −60 to −4° C., b) theorganic phase which is substantially at the reaction temperature isbrought into intimate contact with a first portion of water whosetemperature is at least 80° C. above the reaction temperature, withformation of an emulsion which contains finely dispersed water dropletsin the organic phase, c) a second portion of water is added to theemulsion with formation of a continuous, predominantly organic phase anda continuous, predominantly aqueous phase, and d) the organic phase isseparated from the aqueous phase.
 2. A process as claimed in claim 1, inwhich the sum of the first and second portions of water is from 5 to100% by weight, based on the weight of the organic phase, and the weightratio of the first portion to the second portion is from 1:10 to 10:1.3. A process as claimed in claim 1 or 2, in which the emulsion obtainedby bringing the organic phase into contact with the first portion ofwater has a mixing temperature of from +5 to +50° C.
 4. A process asclaimed in any of the preceding claims, in which the cocatalyst used isa secondary alcohol of 3 to 20 carbon atoms.
 5. A process as claimed inany of the preceding claims, in which polymerization is effected in stepa) until polyisobutene molecules having a number average molecularweight of from 1 800 to 5 000 are obtained.
 6. A process as claimed inany of the preceding claims, in which, in order to separate the organicphase from the aqueous phase, first the main amount of the aqueous phaseis removed, the organic phase containing still dispersed water dropletsis passed through an apparatus having coalescence-promoting internalsand the coalesced aqueous phase is separated from the organic phase. 7.A process as claimed in claim 6, in which the organic phase freed fromthe main amount of the aqueous phase is mixed with a third portion ofwater before the passage through the apparatus havingcoalescence-promoting internals.
 8. A process as claimed in claim 7, inwhich the third portion of water is from 0.5 to 10% by weight, based onthe organic phase.